Genome analysis of a hyper acetone-butanol-ethanol (ABE) producing Clostridium acetobutylicum BKM19

Previously the development of a hyper acetone-butanol-ethanol (ABE) producing Clostridium acetobutylicum BKM19 strain capable of producing 30.5% more total solvent by random mutagenesis of its parental strain PJC4BK, which is a buk mutant C. acetobutylicum ATCC 824 strain is reported. Here, BKM19 and PJC4BK strains are re-sequenced by a high-throughput sequencing technique to understand the mutations responsible for enhanced solvent production. In comparison with the C. acetobutylicum PJC4BK, 13 single nucleotide variants (SNVs), one deletion and one back mutation SNV are identified in the C. acetobutylicum BKM19 genome. Except for one SNV found in the megaplasmid, all mutations are found in the chromosome of BKM19. Among them, a mutation in the thlA gene encoding thiolase is further studied with respect to enzyme activity and butanol production. The mutant thiolase (thlA^V5A) is showed a 32% higher activity than that of the wild-type thiolase (thlA^WT). In batch fermentation, butanol production is increased by 26% and 23% when the thlA^V5A gene is overexpressed in the wild-type C. acetobutylicum ATCC 824 and in its derivative, the thlA-knockdown TKW-A strain, respectively. Based on structural analysis, the mutation in thiolase does not have a direct effect on the regulatory determinant region (RDR). However, the mutation at the 5^th residue seems to influence the stability of the RDR, and thus, increases the enzymatic activity and enhances solvent production in the BKM19 strain.